The present invention relates to multi-speed gear hub systems and more particular to an internal gear hub system shiftable under load for a bicycle.
Internal gear hub systems shiftable under load have devices which make it possible to disengage and engage gearing system elements that are currently in the power flow with little shifting force. This disengagement and engagement of gearing system elements, such as a ring gear, a planet carrier, driver, and clutch components, is preferably accomplished via controllable spring-loaded pawls.
Such a pawl control system is disclosed in DE 2937126 C2 for a two-speed gear hub. A preloaded pawl control member is displaced with relatively little shifting force against spring-loaded pawls by a selector element. The selector element is arranged in the axial direction and is displaceable by a selector rod between two end positions. The pawl control member hooks under the pawls and pivots them, even under load, out of a corresponding pawl tooth set, thereby interrupting the power flow.
Another pawl-controlled multi-speed hub shiftable under load is disclosed in DE 3443592 C2. The hub includes a planetary gear mechanism and a driver that carries a sprocket and is mounted on a hub shaft. The planetary gear mechanism includes a stationary sun gear, a planet carrier with a planet gears, and a ring gear. Four pawl freewheels are located in the power flow respectively between the driver and the ring gear, a selector element and the planet carrier, the ring gear and the hub shell, and the hub shell and a pawl carrier joined rotatably to the planet carrier. The pawls may be disengaged or engaged with corresponding pawl teeth, or overrun when the component having the pawl teeth is rotating faster than the component having the pawls.
To shift to a desired gear ratio, the selector element is slid into the desired ratio by a shift linkage via an axially displaceable actuation element, thus directing the power flow via the corresponding pawls. When the hub is in the high gear ratio, the power introduced into the driver from the sprocket is passed to the selector element and then to the selector element pawls to the planet carrier. The planet gears rotate the ring gear, and the ring gear pawls transfer the power to the hub shell connected to the driven wheel. In the high gear ratio, all the pawls are located opposite the corresponding pawl teeth, and the propulsion pawls and the pawls on the pawl carrier coupled nonrotatably to the planet carrier are overrun by their pawls teeth.
In order to engage the direct and low gear ratios, the actuation element is slid against the selector element. The rotation of the selector element is used to release the selector element pawls from engagement with the planet carrier, thereby greatly reducing the necessary shifting force. The power flow through the selector element is thus interrupted. In the direct gear ratio, the power flow travels from the driver via the driver pawl to the ring gear, and via the ring gear pawl to the hub shell. The pawls on the pawl carrier are overrun by their pawl teeth. In the low gear ratio, the ring gear pawl is additionally disengaged by a stop surface on the selector element, so that the power flow travels from the ring gear via the planet gears to the planet carrier and from there via the pawl carrier and the pawls to the hub shell.
The above mentioned multi-speed hub is shiftable under load but has several shortcomings. One problem is that in some shift positions, the spring-preloaded components with different rotation speeds rub against one another. Another problem is that shifting forces in the direction of the driver act, without a spring buffer, directly on the actuation element and the selector element, resulting in the gear ratio selection being more difficult under unfavorable shifting conditions and the gear ratio preselection is not possible. Another problem is the complex component configurations for the driver, the ring gear and the selector element, making production and assembly difficult.
An object of the present invention is to provide a multi-speed hub shiftable under load that eliminates the aforesaid shortcomings, ensures effective and ratio-independent braking performance, and moreover is easy to produce and assemble.
Specifically, there is to be no difference in rotational speed between the spring-loaded shifting components and the corresponding spring bracing. During unfavorable shifting situations it is desirable to have gear ratio preselection or temporary storage of the shifting force. The operation of switching over from propulsion mode to backpedal braking mode should occur with as little delay as possible, but with a desirable backlash. The braking operation should always occur in the low gear ratio. The configuration of the components are such that the sintered or molded plastic parts may be used, resulting in parts that are produced with as little reworking as possible and are easy to assemble.
The present invention provides these features by having a separate pawl carrier that receives a plurality of pawls directed outward and inward and arranged axially next to the driver, and also having a split ring gear for the receiving and supporting displaceable pawls. The pawl carrier sits on driving segments of the driver and the pawls are located on the periphery of the carrier. The pawls are engagable with the ring gear and are respectively oriented in a first rotational direction or a second rotational direction. The pawls are activated or deactivated by a cam element joined nonrotatably to the driver. The driving segments of the driver rotate the cam element about the hub shaft with zero-backlash. The pawl carrier is rotatable with respect to the driving segments, so that the corresponding spring-loaded pawls on the periphery of the pawl carrier are simultaneously engaged and disengaged by the cam element regardless of rotation direction. The cam element has several open spaces which form a cam profile which partially surrounds the pawls axially and, in the context of a relative rotation of the driver and the pawl carrier, bring about the radial motion of the spring-preloaded pawls.
The spring-preloaded pawls are also provided on the inside diameter of the pawl carrier. These pawls engage a coupler and are longer than a driving contour of the coupler. The pawls are engaged or disengaged via a control contour located on an axially displaceable shifting sleeve that is joined nonrotatably to the hub shaft.
During the shifting operation, the shifting motion of the selector element is transferred via a spacer bushing to the shifting sleeve that is axially preloaded by a spring. The spacer bushing is longer than the inside length of the spring-preloaded coupler. Such a configuration ensures that each shifting operation causes preloading of a spring, which does not execute a gear ratio change until a favorable shifting situation exists. As the selector element is displaced toward the planet gear, a displacement in the same direction of the preloaded shifting sleeve is thus already made possible, while the inwardly directed pawls on the pawl carrier are still engaged in the driving contour of the coupler. The preloaded shifting sleeve has a stop collar, a control contour, and a inclined collar that hold the pawls in the disengaged state. The stop collar diameter corresponds approximately to the root diameter of the driving contour of the coupler. The stop collar serves to pre-center the inwardly directed pawls on the pawl carrier. These pawls extend out beyond the driving teeth of the coupler, and which may result in the pawls being slightly tilted during nonuniform loading or an unfavorable tolerance situation. However, the tilting is compensated for by the pre-centering of the pawls which allows the control contour to hook under the pawls and disengage them from the driving contour on the coupler. The longer pawls allow for easier centering and hooking by the shifting sleeve. The unloaded coupler is then displaced by the shifting sleeve toward the planet gear.
The coupler is nonrotatably connected to the planet carrier for all gear ratios. When the pawls are engaged, power is transferred from the driver to the planet carrier. When the coupler is axially displacement, the pawls in the ring gear, configured as displacement pawls, may be disengaged from the driving contour of the hub shell by a stop surface. The displacement pawls may be mounted by studs in elongated holes on the ring gear, and are preloaded by springs. The ring gear may form two parts. The parts have corresponding facing surfaces being matched to one another to ensure a radial and nonrotatable joint. The two part configuration also facilitates assembly of the stud-mounted displacement pawls and allows the ring gear to be manufactured as a molded part, e.g. sintered part or cold-formed part. The spring-preloaded displacement pawls that couple the ring gear and the hub shell are used to counteract gearing system distortion after a backpedal braking operation. The distortion may occur if the nondisplaceable ring gear pawls and locking pawls located in the power flow between the planet carrier and hub shell are simultaneously engaged in driving contours of the hub shell.
The configuration of the separate pawl carrier, control sleeve, coupler, ring gear, and cam element provides a cost efficient manufacturing, without reworking, of these components as molded parts, e.g. as sintered, forged, cold-formed or molded plastic parts. The configuration also simplifies the assembly of the subassemblies and the hub gearing system.
In the present invention, gear selection of the hub is accomplished exclusively by engaging and disengaging pawls. When the hub is in the low gear ratio, the power flows from the driver via the driving segments to the pawl carrier, via propulsion pawls on the periphery to the ring gear, via planet gears to the planet carrier and from there via pawls to the hub shell. In the low gear position, the pawls between the pawl carrier and the coupler and between the ring gear and the hub shell are disengaged.
When the hub is in the direct gear ratio, the power flows from the driver via the driving segments to the pawl carrier, via propulsion pawls to the ring gear and from there via pawls to the hub shell. In the direct gear ratio, the pawls from the planet carrier to the hub shell and the pawls from the pawl carrier to the ring gear are overrun.
The backpedal brake of the multi-speed hub always operates in the low gear ratio. As the driver is rotated backward, the rotational play between the driving segment and the pawl carrier is taken up, and at the same time the propulsion pawls are disengaged from the cam element and the brake pawls are engaged. The backward rotational motion is transferred from the brake pawls to the ring gear, and then via the planet gears to the planet carrier. The braking motion is then converted into an axial motion by a brake cone or, in the other braking apparatuses, for example into a radial motion by ramp segments and rollers. During the braking operation, the pawls acting on the hub shell and on the coupler are overrun by the corresponding driving contours.
Other objects and features of the present invention will become apparent from the following detailed description considered in conjunction with the accompanying drawings. It is to be understood, however, that the drawings are designed solely for purposes of illustration and not as a definition of the limits of the invention, for which reference should be made to the appended claims. It should be further understood that the drawings are not necessarily drawn to scale and that, unless otherwise indicated, they are merely intended to conceptually illustrate the structures and procedures described herein.